Automatic noise control

1. An active noise control system comprising:

a first active noise control sub-system including at least one loudspeaker and at least one microphone; and

a second active noise control sub-system including at least one additional loudspeaker; wherein:

a first distance between the at least one loudspeaker and the at least one microphone forms a first secondary path;

a second distance between the at least one additional loudspeaker and the at least one microphone forms a second secondary path;

the first distance is shorter than the second distance causing the first active noise control sub-system to have a higher robustness than the second active noise control sub-system;

a seat with a backrest, the backrest enclosing a hollow volume,

wherein the at least one loudspeaker is disposed within the hollow volume of the backrest wherein:

the first active noise control sub-system comprises a first automatic noise sub-controller connected upstream of the at least one loudspeaker disposed in the hollow volume of the backrest.

2. The system of claim 1 , further comprising a stability controller; wherein the stability controller evaluates a stability of the second active noise control sub-system and switches the second active noise control sub-system off or restricts an operation of the active noise control sub-system to lower frequencies when an instability condition of the second active noise control sub-system is detected.

3. The active noise control system of claim 1 , wherein the at least one additional loudspeaker is disposed outside the backrest; wherein the second active noise control sub-system comprises a second automatic noise sub-controller connected upstream of the at least one additional loudspeaker disposed outside the backrest.

4. The active noise control system of claim 1 , wherein the at least one loudspeaker disposed within the hollow volume of the backrest is positioned so that a main radiation axis of the at least one loudspeaker disposed within the hollow volume of the backrest is directed to a listening position where a passenger's head would be when the passenger is sitting on the seat.

5. The active noise control system of claim 1 , wherein the at least one microphone is disposed in an ambience of the at least one loudspeaker disposed within the hollow volume of the backrest and connected upstream of the first automatic noise sub-controller.

6. The active noise control system of claim 1 , wherein the at least one loudspeaker disposed within the hollow volume of the backrest is disposed within at least one enclosure; the enclosure being disposed within the hollow volume of the backrest.

7. The active noise control system of claim 6 , wherein the at least one enclosure has a predetermined breaking point.

8. The active noise control system of claim 1 , wherein the at least one loudspeaker disposed within the hollow volume of the backrest has a main radiation axis; and

the at least one loudspeaker disposed within the hollow volume of the backrest is positioned so that the main radiation axis of the at least one loudspeaker disposed within the hollow volume of the backrest is upward bound, forward bound, or therebetween.

9. The active noise control system of claim 8 , wherein the at least one loudspeaker disposed within the hollow volume of the backrest is positioned so that the main radiation axis of the loudspeaker is directed to a listening position where a passenger's head would be when the passenger is sitting on the seat.

10. The active noise control system of claim 1 , wherein at least one of the first active noise control sub-system and second active noise control sub-system receives a noise reference signal.

11. An active noise control method comprising:

generating with a first active noise control sub-system including at least one loudspeaker and at least one microphone, anti-noise that is configured to reduce or cancel noise occurring at a listening position; and

generating with a second active noise control sub-system including at least one additional loudspeaker, anti-noise that is configured to reduce or cancel noise occurring at the listening position; wherein:

a first distance between the at least one loudspeaker and the at least one microphone forms a first secondary path;

a second distance between the at least one additional loudspeaker and the at least one microphone forms a second secondary path; and

the first distance is shorter than the second distance causing the first active noise control sub-system to have a higher robustness than the second active noise control sub-system,

wherein the listening position is in an ambience of a seat with a backrest that encloses a hollow volume; the method further comprising:

first generating the anti-noise that is configured to reduce or cancel noise occurring at the listening position; and

radiating the anti-noise from within the hollow volume of the backrest of the seat.

12. The active noise control method of claim 11 , further comprising:

evaluating a stability of the second active noise control sub-system; and

switching the second active noise control sub-system off or restricting an operation of the second active noise control sub-system to lower frequencies when an instability condition of the second active noise control sub-system is detected.

13. The active noise control method of claim 11 , further comprising:

generating additional anti-noise that is configured to reduce or cancel noise occurring at the listening position; and

radiating the additional anti-noise from a position outside the seat.

14. An active noise control system comprising:

a first active noise control sub-system including at least one loudspeaker positioned with a seat and at least one microphone;

a second active noise control sub-system including at least one additional loudspeaker; and

a stability controller that evaluates a stability of the second active noise control sub-system and switches the second active noise control sub-system off or restricts an operation of the second active noise control sub-system to lower frequencies when an instability condition of the second active noise control sub-system is detected, wherein:

a first distance between the at least one loudspeaker and the at least one microphone forms a first secondary path;

a second distance between the at least one additional loudspeaker and the at least one microphone forms a second secondary path; and

the first distance is shorter than the second distance causing the first active noise control sub-system to have a higher robustness than the second active noise control sub-system,

wherein:

the seat includes a backrest, the backrest enclosing a hollow volume;

the at least one loudspeaker is disposed within the hollow volume of the backrest and

the first active noise control sub-system comprises a first automatic noise sub-controller connected upstream of the at least one loudspeaker disposed in the hollow volume of the backrest.

15. The active noise control system of claim 14 , wherein the at least one additional loudspeaker is disposed outside the backrest; and wherein the second active noise control sub-system comprises a second automatic noise sub-controller connected upstream of the at least one additional loudspeaker disposed outside the backrest.

16. The active noise control system of claim 14 , wherein the at least one loudspeaker disposed within the hollow volume of the backrest is positioned so that a main radiation axis of the at least one loudspeaker disposed within the hollow volume of the backrest is directed to a listening position where a passenger's head would be when the passenger is sitting on the seat.

17. The active noise control system of claim 14 , wherein the at least one microphone is disposed in an ambience of the at least one loudspeaker disposed within the hollow volume of the backrest and connected upstream of the first automatic noise sub-controller.

18. The active noise control sub-system of claim 1 further including at least one additional microphone disposed in one of the backrest and a headrest.

19. The method of claim 11 further including positioning at least one additional microphone in a one of the backrest and a headrest.

20. The active noise control system of claim 14 further including at least one additional microphone disposed in one of the backrest and a headrest.